Many superalloys have been developed. Of the many superalloys that have been developed, only a few have been adopted for use. Often, the expense of using a new alloy exceeds the benefit associated with using the new alloy. Due to this expense of using a new alloy, the properties of many alloys are not exploited.
In the past, articles have been formed by conventional forging techniques. The conventional forging techniques can be expensive, can only be performed by a few facilities, can result in unusable scrap material, and can be susceptible to cracking, oxidation, and/or contamination by foreign objects.
Alternative to conventional forging techniques, some alloys can be formed through powder metallurgy processes. The powder metallurgy process can include remelting a preliminary ingot then atomizing it into small droplets that solidify as miniature ingots with limited or no segregation of alloy elements. The powders are consolidated by hot isostatic pressing and/or by extrusion and processed to achieve as much as 100% density. The aggregates are generally homogenous and can display uniform properties. Sometimes, the powder can be pressed directly to form a final size/shape, but usually the powder is compacted to an intermediate stage (for example, extruded billet) and forged to final form. Powder metallurgy can be expensive, but can result in savings on subsequent machining costs, the ability to control defects, and the ability to use very high strength compositions.
Alloys formed from powder metallurgy can be difficult to weld. Furthermore, in the past, adding additional alloy to articles formed from powder metallurgy resulted in inconsistent grain structure.